Synthesis and use of precursors for vapor deposition of tungsten containing thin films

ABSTRACT

Methods are provided for synthesizing W(IV) beta-diketonate precursors. Additionally, methods are provided for forming W containing thin films, such as WS2, WNx, WO3, and W via vapor deposition processes, such as atomic layer deposition (ALD) type processes and chemical vapor deposition (CVD) type processes. Methods are also provided for forming 2D materials containing W.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.16/434,834, filed Jun. 7, 2019, which is a continuation of U.S.application Ser. No. 15/729,210, filed Oct. 10, 2017, now U.S. Pat. No.10,358,407, which claims priority to U.S. Provisional Application No.62/407,168, filed Oct. 12, 2016 and U.S. Provisional Application No.62/424,311, filed Nov. 18, 2016 and is related to PCT Application No.PCT/US2016/033955 filed on May 24, 2016, each of which is herebyincorporated by reference.

PARTIES OF JOINT RESEARCH AGREEMENT

The invention claimed herein was made by, or on behalf of, and/or inconnection with a join research agreement between the University ofHelsinki and ASM Microchemistry Oy. The agreement was in effect on andbefore the date the claimed invention was made, and the claimedinvention was made as a result of activities undertaken within the scopeof the agreement.

FIELD

The present application relates generally to precursors and methods forforming thin films comprising tungsten by atomic layer deposition. Suchfilms may find use, for example, as two-dimensional (2D) materials inelectronic devices.

BACKGROUND

Transition metal dichalcogenide materials, especially 2D transitionmetal dichalcogenide materials such as W dichalcogenides have desirableelectronic properties for a variety of applications. Additionally,unlike graphene, another two-dimensional material, certaintwo-dimensional transition metal dichalcogenides have a direct band gapand are semiconducting.

SUMMARY

In some aspects, processes for forming a W containing thin film areprovided. In some embodiments a W containing thin film is formed on asubstrate in a reaction chamber in a process comprising at least onecycle, the cycle comprising contacting the substrate with a vapor phaseW precursor such that at most a molecular monolayer of W containingspecies is formed on the substrate surface, contacting the substratewith a vapor phase second precursor, and optionally repeating the twocontacting steps until a W containing thin film of the desired thicknessis formed. In some embodiments the W in the W precursor has an oxidationstate of +IV. In some embodiments the second precursor reacts with the Wcontaining species on the substrate surface.

In some embodiments the process is an atomic layer deposition (ALD)process. In some embodiments the process is a chemical vapor deposition(CVD) process. In some embodiments the process comprises two or moresequential cycles. In some embodiments the W containing thin film is atungsten oxide, for example WO₃, tungsten nitride, for example WN_(x),tungsten silicide, tungsten carbide, tungsten chalcogenide, for exampleWS₂, or elemental tungsten thin film, or mixtures thereof. In someembodiments the W containing film is a tungsten sulfide, tungstenselenide or tungsten telluride film. In some embodiments the Wcontaining film may be a metallic film, a conducting film, or aninsulating film. In some embodiments the oxidation state of the W in theW precursor is +IV. In some embodiments the W precursor istetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)tungsten(IV), alsoreferred to as W(thd)₄. In some embodiments the second precursorcomprises a chacogenide and may be, for example, H₂S, H₂Se, H₂Te,(CH₃)₂S, (CH₃)₂Se or (CH₃)₂Te

In some aspects, atomic layer deposition (ALD) processes for forming a Wcontaining thin film are provided. According to some embodiments, a Wcontaining thin film is formed on a substrate in a reaction chamber inan ALD process comprising at least one cycle, the cycle comprisingcontacting the substrate with a vapor phase W precursor such that atmost a molecular monolayer of W containing species is formed on thesubstrate surface, removing excess W precursor and reaction byproducts,if any, contacting the substrate with a vapor phase second precursor,removing excess second precursor and reaction byproducts, if any, andrepeating the contacting and removing steps until a W containing thinfilm of the desired thickness is formed. In some embodiments the Wprecursor may comprise a W(IV) beta-diketonate compound. In someembodiments the second precursor reacts with the W containing species onthe substrate surface.

In some embodiments, chemical vapor deposition (CVD) processes forforming a W containing thin film are provided. According to someembodiments a W containing thin film is formed on a substrate in areaction chamber in an CVD process comprising at least one cycle, thecycle comprising contacting the substrate with a vapor phase W precursorpulse. In some embodiments the cycle can also comprise contacting thesubstrate with a vapor phase second precursor pulse, and repeating thecontacting steps until a W containing thin film of the desired thicknessis formed. In some embodiments the W precursor pulse and the secondprecursor pulse may be partially overlapping pulses. In some embodimentsa precursor or precursors may decompose away from the substrate surface.In some embodiments the W precursor may comprise a W(IV)beta-diketonate. In some embodiments the vapor deposition processes forforming a W containing thin film may comprise a pulsed CVD process, or asequential CVD process.

In some aspects, atomic layer deposition (ALD) processes for forming a Wsulfide, such as WS₂, tungsten selenide, or tungsten telluride 2Dmaterial are provided. According to some embodiments, a W sulfide,selenide, or telluride 2D material is formed on a substrate in areaction chamber in an ALD process comprising at least one cycle, thecycle comprising contacting the substrate with a vapor phase W precursorsuch that at most a molecular monolayer of W containing species isformed on the substrate surface, removing excess W precursor andreaction byproducts, if any, contacting the substrate with a vapor phasesulfur, selenium, or tellurium precursor, and removing excess sulfur,tellurium or selenium precursor and reaction byproducts, if any. In someembodiments the W precursor is a W(IV) beta-diketonate precursor. Insome embodiments the sulfur, selenium, or tellurium precursor reactswith the W containing species on the substrate surface.

In some aspects, processes for forming a W sulfide, selenide, ortelluride 2D material are provided. According to some embodiments, a Wsulfide, selenide, or telluride 2D material is formed on a substrate ina reaction chamber in an cyclic process comprising at least one cycle,the cycle comprising contacting the substrate with a vapor phase Wprecursor such that at most a monolayer, less than or equal to about 50%of a monolayer, less than about 25% of a monolayer, or less than about10% of a monolayer of W containing material is formed on the substratesurface; exposing the substrate to purge gas and/or removing excess Wprecursor and reaction byproducts, if any; contacting the substrate witha vapor phase sulfur, selenium, or tellurium precursor; and exposing thesubstrate to purge gas and/or removing excess sulfur, tellurium orselenium precursor and reaction byproducts, if any. In some embodimentsthe W precursor is a W(IV) beta-diketonate precursor. In someembodiments the sulfur, selenium, or tellurium precursor reacts with theW containing material deposited on the substrate surface.

In some embodiments the W containing thin film is a W sulfide, selenide,or telluride thin film, for example a WS₂ thin film. In some embodimentsthe oxidation state of the W atom comprising the W precursor is +IV. Insome embodiments the chalcogen precursor comprises H₂S, H₂Se, H₂Te,(CH₃)₂S, (CH₃)₂Se, (CH₃)₂Te, or (R₃Si)₂E, where R is a hydrocarbon groupand E is S, Se or Te. In some embodiments the W precursor is W(thd)₄ andthe chalcogen precursor is H₂S. In some embodiments the 2D materialcomprises WS₂.

In some embodiments the W containing thin film is a tungsten nitride(WN_(x)), tungsten oxide (WO₃), or W thin film. In some embodiments theW containing film comprises WN_(x), WO₃, WS₂, W, and/or some combinationof the same. In some embodiments WN_(x) thin films may be used inmicroelectronics, for example as a contact material, as a conductivelayer, or as a barrier layer between silicon and other metals, forexample tungsten or copper. In some embodiments WO₃ thin films may beused for X-ray screen phosphor, in gas sensors, or in differentelectrochromic devices.

In some aspects, methods for making W(IV) beta-diketonate precursors areprovided. In some embodiments a W(IV) beta-diketonate precursor isformed by forming a first product by reacting an alkali metal compoundwith a beta-diketone compound in a solvent, adding a W(IV) halide to asolvent to form a W(IV) halide solution, and subsequently adding thefirst product to the W(IV) halide solution. In some embodiments a W(IV)beta-diketonate precursor having the formula W(L)₄ is formed, wherein Lis a beta-diketonato ligand. In some embodiments L comprises tfac, hfac,fod or acac. In some embodiments the process for making a W(IV)beta-diketonate precursor can comprise forming a first product byreacting KH with Hthd in THF, adding WCl₄ to THF to form a WCl₄solution, and subsequently adding the first product to the WCl₄ solutionto thereby form a W(IV) beta-diketonate precursor having the formulatetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)tungsten(IV), orW(thd)₄.

In some aspects, processes for forming a W containing material areprovided. According to some embodiments, a W containing material isformed on a substrate in a reaction chamber by a process comprising atleast one deposition cycle, the cycle comprising alternately andsequentially contacting the substrate with a vapor phase W precursor anda vapor phase second precursor. In some embodiments the W in the Wprecursor has an oxidation state of +IV.

In some embodiments the deposition is repeated two or more times. Insome embodiments excess W precursor and reaction byproducts, if any, areremoved subsequent to contacting the substrate with a vapor phase Wprecursor and prior to contacting the substrate with the vapor phasesecond precursor. In some embodiments excess second precursor andreaction byproducts, if any, are removed subsequent to contacting thesubstrate with a vapor phase second precursor and prior to beginninganother deposition cycle. In some embodiments the substrate is contactedwith a purge gas subsequent to contacting the substrate with the W vaporphase precursor and prior to contacting the substrate with the vaporphase second precursor. In some embodiments the substrate is contactedwith a purge gas subsequent to contacting the substrate with the secondvapor phase precursor and prior to beginning another deposition cycle.In some embodiments the W containing material comprises elemental W. Insome embodiments the W containing material comprises a W oxide material,for example WO₃. In some embodiments the W containing material comprisesa W nitride material, for example WN_(x). In some embodiments the Wcontaining material comprises a W chalcogenide material, for exampleWS₂. In some embodiments the W containing material comprises a Wsilicide material.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the Detailed Descriptionand from the appended drawings, which are meant to illustrate and not tolimit the invention, and wherein:

FIG. 1 is a process flow diagram generally illustrating a method fordepositing a W containing thin film;

FIG. 2 is a process flow diagram generally illustrating a method forsynthesizing a W(IV) beta-diketonate precursor;

FIG. 3 illustrates the molecular structure of a W(thd)₄ as determined bysingle crystal x-ray diffraction;

FIG. 4 illustrates thermoanalytical measurement results, that is, TGA,DTG and SDTA curves for W(thd)₄;

FIG. 5A is an X-ray diffractogram of a WS₂ film formed at 350° C.according to some embodiments;

FIG. 5B is a scanning electron microscope (SEM) image of a WS₂ filmformed at 350° C. according to some embodiments;

FIG. 6A is an X-ray diffractogram of a WS₂ film formed at 500° C.according to some embodiments;

FIG. 6B is a scanning electron microscope (SEM) image of a WS₂ filmformed at 500° C. according to some embodiments;

DETAILED DESCRIPTION

As discussed below, W containing thin films can be deposited on asubstrate by vapor deposition type processes, such as atomic layerdeposition (ALD) and chemical vapor deposition (CVD) type processes. Insome embodiments W containing films such as tungsten oxide, for exampleWO₃; tungsten nitride, for example WN_(x); tungsten chalcogenide, forexample WS₂; tungsten silicide; and/or elemental tungsten films can bedeposited on a substrate by a vapor deposition process, for example anALD or CVD type process. In some embodiments W chalcogenide thin films,particularly W sulfide or selenide thin films can be deposited on asubstrate by ALD or CVD type processes.

Suitable substrate materials may include insulating materials,dielectric materials, crystalline materials, epitaxial, heteroepitaxial,or single crystal materials such as oxides. For example, the substratemay comprise Al₂O₃, sapphire, silicon oxide, or an insulating nitride,such as AlN. Further, the substrate material and/or substrate surfacemay be selected by the skilled artisan to enhance, increase, or maximizetwo-dimensional crystal growth thereon. In some embodiments thesubstrate surface on which the W containing thin film or material is tobe deposited does not comprise semiconductor materials, such as Si, Ge,III-V compounds, for example GaAs and InGaAs, or II-VI compounds. Insome embodiments the substrate surface on which the W containing thinfilm or material is to be deposited may also comprise materials otherthan insulating materials. In some embodiments, after deposition of theW containing thin film, the W containing thin film is removed from atleast a portion of the substrate comprising a material other than aninsulating material. In some embodiments the substrate surface on whichthe W containing thin film or material, such as a W chalcogenide thinfilm or material, is to be deposited comprises a chalcogen, such assulfur, selenium or tellurium. In some embodiments the substrate surfaceon which the W containing thin film or material is to be depositedcomprises surface groups which comprise a chalcogen, such as surfacegroups having chalcogen-hydrogen bonds, such as a —S—H group.

ALD type processes are based on controlled surface reactions ofprecursor chemicals. Gas phase reactions are avoided by alternately andsequentially contacting the substrate with the precursors. Vapor phasereactants are separated from each other on the substrate surface, forexample, by removing excess reactants and/or reactant byproducts fromthe reaction chamber between reactant pulses.

CVD type processes typically involve gas phase reactions between two ormore reactants. The reactants can be provided simultaneously to thereaction space or substrate. The substrate or reaction space can beheated to promote the reaction between the gaseous reactants. CVDdeposition occurs when the reactants or precursors are provided to thereaction space or substrate. In some embodiments the reactants areprovided until a thin film having a desired thickness is deposited. Insome embodiments cyclical CVD type processes can be used with multiplecycles used to deposit a thin film having a desired thickness. In someembodiments one or more plasma reactants can be used in the CVD process.

In some embodiments an ALD-process can be modified to be a partial CVDprocesses. In some embodiments a partial CVD process can include atleast partial decomposition of one or more precursors. In someembodiments ALD processes can be modified to be a pulsed CVD processes.In some embodiments an ALD process is modified to use overlapping orpartially overlapping pulses of reactants. In some embodiments an ALDprocess is modified to use extremely short purge or removal times, suchas below 0.1 s (depending on the reactor). In some embodiments an ALDprocess is modified to use extremely long or continuous pulse times. Forexample, in some embodiments an ALD process is modified to use no purgeor removal at all after at least one pulse. In some embodiments no purgeis used after a W precursors pulse. In some embodiments no purge is usedafter an second precursor pulse. In some embodiments no purge is usedafter either a W precursor pulse or a second precursor pulse.

In some embodiments a single W precursor is utilized. Thus, in someembodiments the process may not include contacting the substrate with avapor phase second reactant. In some embodiments a substrate is exposedto one precursor pulse, or sequential precursor pulses separate by aprecursor removal or purge step. For example, in some embodiments asubstrate may be continuously or intermittently contacted with a vaporphase W precursor and not with a vapor phase second reactant (or anyadditional reactants). Although in some embodiments a substrate may becontacted by another species that does not react, such as an inert purgegas or carrier gas, in addition to the vapor phase W precursor. In someembodiments a deposition process may include only one W precursor pulse.

In some embodiments the substrate may be contacted with a vapor phase Wprecursor. Subsequently, excess W precursor and reaction byproducts, ifany, may be removed from the substrate surface, and the substrate mayagain be contacted with a vapor phase W precursor, for example in asequential pulse. The W precursor may be the same in both pulses, ordifferent. In some embodiments the substrate may not contacted with asecond reactant, or any additional reactant. Although in someembodiments a substrate may be contacted by another species that doesnot react, such as an inert purge gas or carrier gas, in addition to thevapor phase W precursor.

Regarding ALD-type processes, briefly, a substrate is heated to asuitable deposition temperature, generally at lowered pressure.Deposition temperatures are generally maintained below the thermaldecomposition temperature of the reactants but at a high enough level toavoid condensation of reactants and to provide the activation energy forthe desired surface reactions. Of course, the appropriate temperaturewindow for any given ALD reaction will depend upon the surfacetermination and reactant species involved. Here, the temperature variesdepending on the type of film being deposited and particular precursors.In some embodiments the deposition temperature may be from about 50° C.to about 800° C., from about 100° C. to about 700° C., from about 200°C. to about 600° C., or from about 300° C. to about 500° C. In someembodiments the deposition temperature may be at or above about 100° C.,at or above about 200° C., at or above about 300° C., or at or aboveabout 350° C. or higher, for example up to about 1000° C. In someembodiments the deposition temperature may be up to about 1000° C., upto about 700° C., or up to about 600° C.

In some embodiments the deposition temperature may be above thedecomposition temperature of a reactant. In some embodiments thedeposition temperature is above the decomposition temperature of the Wreactant but still low enough to maintain reasonably surface controlledgrowth of a film and a growth rate which is greater than 0 but less thanor equal to about a monolayer of material per deposition cycle. In someembodiments a deposition cycle growth rate may be greater than 0 butless than or equal to about 50%, less than about 25%, or less than about10% of about a complete monolayer of material being deposited per cycle.In some embodiments a complete monolayer is one in which all availablereactive sites are occupied. In some embodiments the growth rate of ALDprocess is greater than 0 but less than about 2 Å/cycle, less than about1 Å/cycle, less than about 0.5 Å/cycle, less than about 0.1 Å/cycle,less than about 0.05 Å/cycle or in some instances less than about 0.02Å/cycle. In other embodiments the growth rate of process other than pureALD may be more than about 0.02 Å/cycle, more than about 0.05 Å/cycle,more than about 0.1 Å/cycle, more than about 0.5 Å/cycle, more thanabout 1 Å/cycle, or more than about 2 Å/cycle or greater, up to amaximum growth rate as would be understood by the skilled artisan giventhe deposition conditions of the processes described herein.

In some embodiments a deposition process may not be a pure ALD process.In some embodiments a second precursor may flow continuously orsubstantially continuously through a reaction space throughout adeposition process. For example, the flow rate of a second precursorthrough a reaction space may be reduced while the substrate is contactedwith a W precursor. In some embodiments where a second precursor mayflow continuously, the growth rate of the film per cycle is greater than0 but less than or equal to about one monolayer of the material beingdeposited. In some embodiments where the second precursor flowscontinuously, the growth rate per cycle is greater than 0 but less thanor equal to about 50%, less than about 25%, or less than about 10% of acomplete monolayer of the material being deposited.

The surface of the substrate is contacted with a vapor phase firstreactant. In some embodiments a pulse of vapor phase first reactant isprovided to a reaction space containing the substrate. In someembodiments the substrate is moved to a reaction space containing vaporphase first reactant. Conditions are typically selected such that nomore than about one monolayer of W containing species from the firstreactant is adsorbed on the substrate surface in a self-limiting manner.The appropriate contacting times can be readily determined by theskilled artisan based on the particular circumstances. Excess firstreactant and reaction byproducts, if any, are removed from the substratesurface, such as by purging with an inert gas or by removing thesubstrate from the presence of the first reactant.

Purging means that vapor phase precursors and/or vapor phase byproductsare removed from the substrate surface such as by evacuating a chamberwith a vacuum pump and/or by replacing the gas inside a reactor with aninert gas such as argon or nitrogen. Typical purging times are fromabout 0.05 to 20 seconds, between about 0.2 and 10, or between about 0.5and 5 seconds. However, other purge times can be utilized if necessary,such as where highly conformal step coverage over extremely high aspectratio structures or other structures with complex surface morphology isneeded, or where different reactor types may be used, such as a batchreactor.

The surface of the substrate is contacted with a vapor phase secondgaseous reactant or precursor. The second reactant may react with the Wcontaining species from the first reactant that are present on thesubstrate surface. In some embodiments a pulse of a second gaseousreactant is provided to a reaction space containing the substrate. Thevapor phase second gaseous reactant may be provided into the reactionchamber in a substantially continuous flow from a reaction chamber inletto an outlet. In some embodiments outlet flow from the reaction chamber,for example a pump line, is not closed. In some embodiments outlet flowfrom the reaction chamber, for example flow from a reaction chamber to apump line and further through the pump line prior to the pump, is notsubstantially closed, but may be restricted. In some embodiments thesubstrate is moved to a reaction space containing the vapor phase secondreactant. Excess second reactant and gaseous byproducts of the surfacereaction, if any, are removed from the substrate surface. In someembodiments there is no dwell time for the reactants. In someembodiments a vapor phase reactant is not static in the reaction spacewhile the vapor phase reactant is contacting the substrate. A vaporphase reactant may be static when the reactant is not experiencing flowrelative to the substrate, or when the reactant is flowing into thereaction space from one inlet, with no open outlet.

The steps of contacting and removing are repeated until a thin film ofthe desired thickness has been selectively formed on the substrate, witheach cycle leaving no more than about a molecular monolayer. The stepsof contacting and removing a first vapor phase W precursor may bereferred to as a first precursor phase, a W precursor phase, or a Wphase. The steps of contacting and removing a second vapor phaseprecursor may be referred to as a second precursor phase. Together,these two phases can make up a deposition cycle. Additional phasescomprising alternately and sequentially contacting the surface of asubstrate with other reactants can be included to form more complicatedmaterials, such as ternary materials.

As mentioned above, in some embodiments each phase of each cycle may begenerally self-limiting. In some embodiments an excess of reactantprecursors is supplied in each phase to saturate the susceptiblestructure surfaces. Surface saturation ensures reactant occupation ofessentially all available reactive sites (subject, for example, tophysical size or “steric hindrance” restraints) and thus ensuresexcellent step coverage and uniformity. Typically, some material, butless than one molecular layer of material, is deposited with each cycle,however, in some embodiments more than one molecular layer is depositedduring the cycle.

Removing excess reactants can include evacuating some of the contents ofa reaction space and/or purging a reaction space with helium, nitrogenor another inert gas. In some embodiments purging can comprise turningoff the flow of the reactive gas while continuing to flow an inertcarrier gas to the reaction space.

The precursors employed in the ALD type processes may be solid, liquidor gaseous materials under standard conditions (room temperature andatmospheric pressure), provided that the precursors are in vapor phasebefore they are contacted with the substrate surface. Contacting asubstrate surface with a vaporized precursor means that the precursorvapor is in contact with the substrate surface for a limited period oftime. Typically contacting times are from about 0.05 to 20 seconds,between about 0.2 and 10, or between about 0.5 and 5 seconds. In someembodiments the vapor phase second gaseous contacting time is of thesame order of magnitude as the vapor phase first gaseous reactantcontacting time. In some embodiments the vapor phase second gaseouscontacting time is no more than about 100 times longer than the vaporphase first gaseous reactant contacting time.

However, depending on the substrate type and its surface area, thecontacting time may be even higher than 20 seconds. Contacting times canbe on the order of minutes in some cases. The optimum contacting timecan be determined by the skilled artisan based on the particularcircumstances. In some embodiments the second precursor contacting timeis greater than 0, but less than about 60 seconds, less than about 30seconds, less than about 10 seconds, or less than about 5 seconds.

The mass flow rate of the precursors can also be determined by theskilled artisan. In some embodiments the flow rate of a W precursor isbetween about 1 and 1000 sccm without limitation, or between about 100and 500 sccm.

The pressure in a reaction chamber is typically from about 0.01 to about50 mbar, or from about 0.1 to about 10 mbar. However, in some cases thepressure will be higher or lower than this range, as can be determinedby the skilled artisan given the particular circumstances.

Before starting the deposition of the film, the substrate is typicallyheated to a suitable growth temperature. The growth temperature variesdepending on the type of thin film formed, physical properties of theprecursors, etc. In some embodiments the growth temperature may be fromabout 50° C. to about 800° C., from about 100° C. to about 700° C., fromabout 200° C. to about 600° C., or from about 300° C. to about 500° C.In some embodiments the growth temperature may be at or above about 100°C., at or above about 200° C., at or above about 300° C., or at or aboveabout 350° C. or higher, for example up to about 1000° C. In someembodiments the growth temperature may be up to about 1000° C., up toabout 700° C., or up to about 600° C. In some embodiments the growthtemperature may be above the decomposition temperature of the Wprecursor. For example, in some embodiments the growth temperature maybe above the decomposition temperature of W(thd)₄.

The growth temperature can be less than the crystallization temperaturefor the deposited materials such that an amorphous thin film is formedor it can be above the crystallization temperature such that acrystalline thin film is formed.

In some embodiments the deposition temperature may vary depending on anumber of factors such as, and without limitation, the reactantprecursors, the pressure, flow rate, the arrangement of the reactor,crystallization temperature of the deposited thin film, and thecomposition of the substrate including the nature of the material to bedeposited on. The specific growth temperature may be selected by theskilled artisan. It is to be noted that the thermal budget, that is areaction temperature and optionally an anneal temperature, duringdeposition and at any point in further processing after the depositionfor films of the present invention is can be less than about 800° C.,less than about 650° C., less than about 600° C., or in some instancesless than about 500° C., but above about 50° C.

In some embodiments the deposited W containing thin film may besubjected to optional post deposition treatment process. In someembodiments, for example, a post deposition treatment process maycomprise an annealing process, for example a forming gas annealingprocess. In some embodiments a post deposition treatment process maycomprise exposing the W containing thin film or material surface to aplasma In some other embodiments a post deposition treatment processdoes not comprise exposing the W containing thin film or materialsurface to a plasma.

Examples of suitable reactors that may be used include commerciallyavailable ALD equipment such as the F-120® reactor, Eagle® XP8, Pulsar®reactor and Advance® 400 Series reactor, available from ASM America,Inc. of Phoenix, Ariz., ASM Japan KK, Tokyo, Japan and ASM Europe B.V.,Almere, Netherlands. In addition to these ALD reactors, many other kindsof reactors capable of ALD growth of thin films, including CVD reactorsequipped with appropriate equipment and means for pulsing the precursorscan be employed. In some embodiments a flow type ALD reactor is used. Insome embodiments reactants are kept separate until reaching the reactionchamber, such that shared lines for the precursors are minimized.However, other arrangements are possible, such as the use of apre-reaction chamber as described in U.S. patent application Ser. No.10/929,348, filed Aug. 30, 2004 and Ser. No. 09/836,674, filed Apr. 16,2001, the disclosures of which are incorporated herein by reference.

In some embodiments a suitable reactor may be a batch reactor and maycontain more than about 25 substrates, more than about 50 substrates ormore than about 100 substrates. In some embodiments a suitable reactormay be a mini-batch reactor and may contain from about 2 to about 20substrates, from about 3 to about 15 substrates or from about 4 to about10 substrates.

The growth processes can optionally be carried out in a reactor orreaction space connected to a cluster tool. In a cluster tool, becauseeach reaction space is dedicated to one type of process, the temperatureof the reaction space in each module can be kept constant, whichimproves the throughput compared to a reactor in which the substrate isheated up to the process temperature before each run.

A stand-alone reactor can be equipped with a load-lock. In that case, itis not necessary to cool down the reaction space between each run.

According to some embodiments, and illustrated in FIG. 1, a W containingthin film is formed on a substrate by an ALD type process comprising atleast one deposition cycle 10 the deposition cycle comprising:

contacting the surface of a substrate with a vaporized W(IV)beta-diketonate precursor at step 12 to adsorb at most a molecularmonolayer of W containing species on the substrate surface;

removing excess W precursor and reaction by products, if any, from thesurface at step 13;

contacting the surface of the substrate with a vaporized secondprecursor at step 14, wherein the second precursor reacts with the Wcontaining species on the substrate surface; and

removing from the surface excess second precursor and any gaseousby-products formed in the reaction between the W precursor layer and thesecond precursor at step 15.

The contacting and removing steps can be repeated 16 until a Wcontaining thin film of the desired thickness has been formed.

Although the illustrated deposition cycle begins with contacting thesurface of the substrate with the W precursor, in other embodiments thedeposition cycle begins with contacting the surface of the substratewith the second precursor. It will be understood by the skilled artisanthat if the surface of the substrate is contacted with a first precursorand that precursor does not react then the process will begin when thenext precursor is provided. In some embodiments, the reactants andreaction by-products can be removed from the substrate surface bystopping the flow of W precursor while continuing the flow of an inertcarrier gas such as nitrogen or argon.

In some embodiments, the reactants and reaction by-products can beremoved from the substrate surface by stopping the flow of secondreactant while continuing the flow of an inert carrier gas. In someembodiments the substrate is moved such that different reactantsalternately and sequentially contact the surface of the substrate in adesired sequence for a desired time. In some embodiments the removingsteps are not performed. In some embodiments no reactant may be removedfrom the various parts of a chamber. In some embodiments the substrateis moved from a part of the chamber containing a first precursor toanother part of the chamber containing the second precursor. In someembodiments the substrate is moved from a first reaction chamber to asecond, different reaction chamber.

In some embodiments the deposited W containing film may comprise atungsten oxide, for example WO₃, tungsten nitride, for example WN_(x),tungsten chalcogenide, for example WS₂, tungsten silicide, and/orelemental tungsten thin film. In some embodiments the deposited Wcontaining film may comprise a dichalcogenide thin film. In someembodiments the deposited thin film may comprise a tungstendichalcogenide. In some embodiments the deposited thin film may compriseWS₂, WSe₂, or WTe₂. For simplicity, these dichalcogenides have beenindicated to have these general stoichiometries, but it will beunderstood that the exact stoichiometry of any given W containing filmor material will vary based on the oxidation state of the elementsinvolved. Accordingly, other stoichiometries are expressly contemplated.

Although the term “dichalcogenide” is used herein and thesedichalcogenides are indicated to have general stoichiometries with theratio of metal atoms, such as W, to chalcogen atoms, such as S, Se, orTe, of 1:2, the stoichiometry of the films may vary. For example theratio of metal atoms to chalcogen atoms may vary due to the analysistechniques used and/or the process conditions. In some embodiments theratio of metal atoms to chalcogen atoms can be from about 1:3 to about2:1, from about 1:2.5 to about 1:1, or from about to 1:2. In someembodiments the dichalcogenide film may contain from about 20 at-% toabout 50 at-%, or from about 25 at-% to about 40 at-% of W. In someembodiments the dichalcogenide film may contain from about 30 at-% toabout 75 at-%, or from about 35 at-% to about 70 at-% of a chalcogen (S,Se or Te).

In some embodiments the W containing dichalcogenide film may containelements other than W and chalcogens. In some embodiments the Wcontaining dichalcogenide film may contain a total of less than about 35at-% of elements, including hydrogen, other than W and chalcogens, ortotal of less than about 25 at-%. In some embodiments the film maycontain less than about 20 at-% carbon, less than about 15 at-% carbon,or less than about 10 at-% carbon. In some embodiments the film maycontain less than about 15 at-% hydrogen, less than about 10 at-%hydrogen, or less than about 5 at-% hydrogen. In some embodiments thefilm may contain less than about 10 at-% oxygen, less than about 5 at-%oxygen, or less than about 3 at-% oxygen. In some embodiments the filmmay contain less than about 10 at-%, less than about 5 at-%, or lessthan about 3 at-% of elements other than W, chalcogens, hydrogen, carbonor oxygen. It is to be noted that a W containing film containing theabove described elements may still be suitable for differentapplications, such as for a 2D-material.

In some embodiments the deposited W containing film may compriseadditional elements other than W, chalcogens (S, Te or Se), oxygen,nitrogen, and/or silicon. In some embodiments the deposited W containingfilm may comprise a dopant. In some embodiments the deposited Wcontaining film may comprise two or more of the elements of the group ofchalcogens (S, Te or Se), oxygen, nitrogen or silicon. In someembodiments the deposited W chalcogenide containing film may comprisetwo or more of the elements of the group of chalcogens (S, Te or Se). Insome embodiments the thin films of the present disclosure can includeany number of metals. According to some embodiments W containing filmsmay include two or more metals. In some embodiments, additionaldeposition phases are added to one or more deposition cycles toincorporate an additional metal or metals into a W containing thin film.An additional metal phase or phases may follow the first metal phase orfollow the second phase, or may follow both phases. In some embodimentstwo or more different metal precursors may be provided simultaneously inthe same metal phase of a deposition cycle. In some embodiments metalprecursors comprising different metals may be used in differentdeposition cycles. For example, a first metal precursor may be the onlymetal precursor used in one or more deposition cycles and a second metalprecursor comprising a second, different metal, may be used in one ormore other deposition cycles.

Referring again to FIG. 1, some embodiments may include an optionalpretreatment process at step 11 applied to the substrate surface. Apretreatment process may comprise one or more steps. In thepretreatment, the substrate surface on which W containing thin film isto be deposited may be exposed to one or more pretreatment reactantsand/or to specific conditions, such as temperature or pressure. Apretreatment may be used for any number of reasons including to cleanthe substrate surface, remove impurities, remove native oxide, andprovide desirable surface terminations. In some embodiments, apretreatment comprises exposing the substrate surface to one or morepretreatment reactant, such as (NH₄)₂S, H₂S, HCl, HBr, Cl₂, or HF. Insome embodiments, a pretreatment process is carried out at about thesame temperature as the subsequent deposition process.

As described below, a number of different precursors can be used todeposit W containing thin films. In some embodiments the W precursor hasa formula of W(thd)₄, wherein thd is2,2,6,6-tetramethyl-3,5-heptanedionato. In some embodiments the secondprecursor is one of H₂S or H₂Se. In some embodiments the W precursor isW(thd)₄, the second precursor is H₂S, and the resultant W containingthin film is a WS₂ thin film.

In some embodiments a WS₂ thin film is formed on a substrate by an ALDtype process comprising at least one deposition cycle comprising:

contacting the surface of a substrate with vaporized W(thd)₄ to a atmost a molecular monolayer of W containing species on the substrate;

removing excess W(thd)₄ and reaction by products, if any, from thesurface;

contacting the surface of the substrate with vaporized H₂S; and

removing from the surface excess H₂S and any gaseous by-products formedin the reaction between the W containing species layer and the H₂S.

The contacting and removing steps can be repeated until a WS₂ thin filmof the desired thickness has been formed.

In some embodiments a W containing thin film may be formed on asubstrate by a vapor deposition process comprising contacting thesubstrate with a vaporized W(IV) beta-diketonate precursor. In someembodiments the process can optionally including contacting thesubstrate with a second precursor, such as a vapor phase secondprecursor. In some embodiments the vapor deposition process may be achemical vapor deposition (CVD) process, a pulsed CVD process, asequential CVD process, an ALD process, or any other type ofchemical-reaction based vapor deposition process.

W Precursors

In some embodiments the W of the W precursor has an oxidation state of+IV. In some embodiments the W precursor may comprise fourbeta-diketonato ligands. In some embodiments the W precursor maycomprise a W(IV) beta-diketonate compound. In some embodiments the Wprecursor does not comprise one or more halide ligands. In someembodiments the W precursor may comprise at least one beta-diketonateligand. In some embodiments the W precursor may comprise at least onebidentante ligand which is bonded to W through at least one oxygen atom.In some embodiments the W precursor may comprise W(acac)₄ where acac isan acetylacetone ligand, W(hfac)₄ where hfac is ahexafluoroacetylacetone ligand, or W(thd)₄ where thd is a2,2,6,6-tetramethyl-3,5-heptanedionato ligand. In some embodiments the Win the W precursor may comprise an oxidation state of +IV and may not beoxidized during the formation of the resultant thin film, whereupon theW has an oxidation state of +IV.

In some embodiments the W precursor is vaporized without solvent. Insome embodiments the W precursor is not mixed with solvent, such asorganic solvent.

In some embodiments W(IV) beta-diketonates may be used in vapordeposition type processes to deposit any kind of W containing thin film.In some embodiments W(IV) beta-diketonates may be used in ALD typeprocesses to deposit any kind of W containing thin film. In someembodiments W(IV) beta-diketonates may be used in CVD type processes todeposit any kind of W containing thin film. In some embodiments Wbeta-diketonates may be used to deposit elemental W films, W sulfidefilms, W oxide films, W nitride films, or W silicide films. Inparticular, W(thd)₄ may be used in ALD and CVD type processes to depositany kind of W containing thin film.

In some embodiments an elemental W thin film may be formed on asubstrate by an ALD type process comprising at least one depositioncycle comprising:

contacting the surface of a substrate with vaporized W(IV)beta-diketonate precursor to form at most a molecular monolayer of Wcontaining species on the substrate;

removing excess W(IV) beta-diketonate precursor and reaction byproducts, if any, from the surface;

contacting the surface of the substrate with a second reactant, such asH₂, or hydrogen plasma, radicals, or atoms; and

removing from the surface excess second reactant and any gaseousby-products formed in the reaction between the W containing specieslayer and the second reactant.

The contacting and removing steps can be repeated until an elemental Wthin film of the desired thickness has been formed.

In some embodiments a W oxide thin film may be formed on a substrate byan ALD type process comprising at least one deposition cycle comprising:

contacting the surface of a substrate with vaporized W(IV)beta-diketonate precursor to form at most a molecular monolayer of Wcontaining species on the substrate;

removing excess W(IV) beta-diketonate precursor and reaction byproducts, if any, from the surface;

contacting the surface of the substrate with an oxygen precursor, suchas water, ozone, or oxygen plasma, radicals, or atoms; and

removing from the surface excess oxygen precursor and any gaseousby-products formed in the reaction between the W containing specieslayer and the oxygen precursor.

The contacting and removing steps can be repeated until a W oxide thinfilm of the desired thickness has been formed.

In some embodiments a W nitride thin film may be formed on a substrateby an ALD type process comprising at least one deposition cyclecomprising:

contacting the surface of a substrate with vaporized W(IV)beta-diketonate precursor to form at most a molecular monolayer of Wcontaining species on the substrate;

removing excess W(IV) beta-diketonate precursor and reaction byproducts, if any, from the surface;

contacting the surface of the substrate with a precursor comprisingnitrogen; and

removing from the surface excess nitrogen precursor and any gaseousby-products formed in the reaction between the W containing specieslayer and the precursor comprising nitrogen.

The contacting and removing steps can be repeated until a W nitride thinfilm of the desired thickness has been formed.

In some embodiments a suitable precursor comprising nitrogen may includeNH₃. In some embodiments a suitable precursor comprising nitrogen mayinclude nitrogen containing plasmas, such as N-plasma, atoms, orradicals or N and H containing plasma, atoms, or radicals.

In some embodiments a W sulfide thin film may be formed on a substrateby an ALD type process comprising at least one deposition cyclecomprising:

contacting the surface of a substrate with vaporized W(IV)beta-diketonate precursor to form at most a molecular monolayer of Wcontaining species on the substrate;

removing excess W(IV) beta-diketonate precursor and reaction byproducts, if any, from the surface;

contacting the surface of the substrate with an precursor comprisingsulfur; and

removing from the surface excess precursor comprising sulfur and anygaseous by-products formed in the reaction between the W containingspecies layer and the precursor comprising silicon.

The contacting and removing steps can be repeated until a W sulfide thinfilm of the desired thickness has been formed.

In some embodiments suitable precursors comprising sulfur may includeH₂S or (CH₃)₂S, among other.

In some embodiments a W containing material may be formed on a substrateby a process comprising at least one deposition cycle, the depositioncycle comprising alternately and sequentially contacting the substratewith a vapor phase W precursor and a vapor phase second precursor. Insome embodiments the deposition cycle may be repeated two or more times.In some embodiments the deposition cycle may be repeated two or moretimes sequentially. In some embodiments excess W precursor and reactionbyproducts, if any, may be removed subsequent to contacting thesubstrate with a vapor phase W precursor and prior to contacting thesubstrate with the vapor phase second precursor. In some embodimentsexcess second precursor and reaction byproducts, if any, may be removedsubsequent to contacting the substrate with a vapor phase secondprecursor and prior to beginning another deposition cycle. In someembodiments the substrate may be contacted with a purge gas subsequentto contacting the substrate with the W vapor phase precursor and priorto contacting the substrate with the vapor phase second precursor. Insome embodiments the substrate may be contacted with a purge gassubsequent to contacting the substrate with the second vapor phaseprecursor prior to beginning another deposition cycle.

Synthesis of W(IV) Beta-Diketonate Precursors

Methods are provided for making the W precursors used in the vapordeposition processes described herein. In some embodiments precursorsare synthesized having a formula of W(L)₄, wherein L is abeta-diketonato ligand, such as acac, tfac, hfac, fod or thd. In someembodiments the W precursor that is synthesized has a formula ofW(thd)₄.

In some embodiments all handling and manipulation may be carried out inan atmosphere that does not comprise air, oxygen, or moisture. In someembodiments all handling and manipulation may be carried out in an inertgas atmosphere, for example a N₂ or Ar atmosphere.

FIG. 2 is a process flow diagram generally illustrating methods forforming W(IV) beta-diketonate precursors 20. In some embodiments theprocess for making a W(IV) beta-diketonate precursor comprises:

forming a first product by reacting an alkali metal compound with abeta-diketone compound in a solvent at step 21;

adding a W(IV) halide to a solvent at step 22 to form a W(IV) halidesolution;

subsequently adding the first product to the W(IV) halide solution atstep 23, thereby forming a W(IV) beta-diketonate precursor at step 24having the formula W(L)₄, wherein L is a beta-diketonato ligand.

In some embodiments the alkali metal compound of step 21 may comprise,for example KH, NaH, BuLi, or MeLi. In some embodiments the alkali metalcompound of step 21 is potassium hydride (KH). In some embodiments thealkali metal compound may be added to a solvent. In some embodiments thesolvent may comprise a heterocyclic solvent. In some embodiments thesolvent is THF.

In some embodiments the beta-diketone compound of step 21 may compriseHthd; Hacac; Htfac, where Htfac is trifluoroacetylacetone; Hfod, wherefod is 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedione; or Hhfac,where Hhfac is hexafluoroacetylacetone. In some embodiments reacting analkali metal compound with a beta-diketone compound may comprise addingthe beta-diketone compound, or a mixture comprising the beta-diketonecompound, to the solution comprising the alkali metal compound tothereby form a first product having the formula M¹L, wherein M¹ is analkali metal and L is a beta-diketonato ligand. In some embodiments KHis added to THF to form a solution. Hthd is then added to the solutionto react with the KH and thereby form a first product comprising K(thd).

In some embodiments the solution may be stirred until the reaction iscomplete. In some embodiments the mixture is stirred for a firstduration. In some embodiments any gaseous by-products produced by thereaction may be exhausted, for example through a bubbler, such as amercury bubbler.

In some embodiments the W(IV) halide of step 22 is an anhydrous W(IV)halide. In some embodiments the W(IV) halide of step 22 has the formulaWX₄, wherein X is a halide, for example Cl. In some embodiments thesolvent of step 22 may comprise a heterocyclic solvent. In someembodiments the solvent of step 22 is THF. Thus, in some embodimentsWCl₄ is added to THF at step 22. In some embodiments the solvent isoptionally cooled prior to, during, and/or after the W(IV) halide isadded. In some embodiments the solvent, for example THF may be cooledprior to the addition of the W(IV) halide compound.

In some embodiments approximately 4 equivalents of the first product areadded to 1 equivalent of the product(IV) halide solution, therebyforming a W(IV) beta-diketonate precursor having the formula ML₄,wherein L is a beta-diketonato ligand. In some embodiments the W(IV)halide solution may be cooled prior to the addition of the firstproduct. In some embodiments, after the addition of the first product,the mixture is allowed to warm to room temperature. In some embodimentsthe mixture is stirred for a second duration. In some embodiments themixture is stirred until the reaction is complete.

After the reaction is substantially complete, the final product isseparated and isolated from any solvents, by-products, excess reactants,or any other compounds that are not desired in the final product.

In some embodiments a W(IV) beta-diketonate precursor may be formed byreacting a W(IV) halide with a compound comprising a beta-diketonatoligand. In some embodiments the compound comprising a beta-diketanatoligand may have the formula M¹L, wherein M¹ is an alkali metal and L isa beta-diketonato ligand. In some embodiments a W(IV) beta-diketonateprecursor may be formed by adding a compound comprising abeta-diketonato ligand to a solution comprising a W(IV) halide such thatthe compounds react to form a W(IV) beta-diketonate precursor. In someembodiments a W(IV) beta-diketonate precursor may be formed by adding aW(IV) halide to a solution comprising a compound comprising abeta-diketonato ligand such that the compounds react to form a W(IV)beta-diketonate precursor. In some embodiments a W(IV) halide compoundand a compound comprising a W(IV) beta-diketonato ligand maysimultaneously, or substantially simultaneously be added to a solventsuch that they react to form a W(IV) beta-diketonate precursor. In someembodiments one or more of the compounds and or solvents may be cooledbefore or during the reaction process.

In some embodiments the process for making a W(IV) beta-diketonateprecursor comprises:

forming a first product by reacting KH with Hthd in THF at step 21;

adding a WCl₄ to THF at step 22 to form a WCl₄ solution;

subsequently adding the first product to the WCl₄ solution at step 23,thereby forming a W(IV) beta-diketonate precursor at step 24 having theformula W(thd)₄.

Example 1

W(thd)₄ was synthesized by the following process. All handling andmanipulation was done under the rigorous exclusion of air and moistureusing standard Schlenk techniques and an inert gas (N₂ or Ar) glove box.

First, 4.59 g (114.44 mmol) of potassium hydride (KH) was added to 100ml of tetrahydrofuran (THF). A stoichiometric amount, 21.09 g (114.44mmol), of 2,2,6,6-tetramethylheptane-3,5-dione (Hthd) was added to 100ml of THF. The Hthd dissolved in 100 ml of THF was added dropwise to theKH and THF mixture while stirring. Evolved H₂ gas released during theprocedure was released through a mercury bubbler. The resultant mixturewas stirred for 4 hours at room temperature to form a potassium2,2,6,6-tetramethylheptane-3,5-dione (K(thd)) solution.

9.32 g (28.61 mmol) of WCl₄ was suspended in 200 ml of THF and cooled to−10° C. The prepared K(thd) solution was added to the suspension of WCl₄while stirring using Ar pressure and a Teflon cannula. This mixture wasallowed to warm to room temperature and was stirred overnight. Themixture was evaporated until dry, leaving a black residue that wastransferred to a sublimator and sublimed out at a temperature of 210° C.and a pressure of 0.5 mbar. The resultant W(thd)₄ sublimate wascollected in the glove box.

The synthesized compound was analyzed using mass spectrometry. Amolecular ion with an isotopic pattern corresponding to [W(thd)₄]⁺ wasseen at m/z 917. In addition to molecular ion [W(thd)₄]⁺, [W(thd)₃]⁺ andother fragment ions, several peaks corresponding to fragment ions withoxygen, such as [W(thd)₃O]⁺, [W(thd)₂(OH)₃]⁺, and [W(thd)₂O₂]⁺, can beseen. However, these oxygen containing peaks are likely due to exposureof the W(thd)₄ compound to air during sample loading into the massspectrometer.

The molecular structure of the synthesized compound was analyzed usingsingle crystal x-ray diffraction (SCXRD). The structure of thesynthesized W(thd)₄ compound is illustrated in FIG. 3.

The thermal properties of W(thd)₄ were investigated usingthermogravimetric analysis (TGA). As shown in FIG. 4, thermogravimetric(TG), derivative thermogravimetric (DTG), and single differentialthermal analysis (SDTA) curves for W(thd)₄ show a single stepevaporation of the compound at about 220° C. to 330° C. The curves alsoshow a 5.5% residue at 600° C. However, in some embodiments, there maybe less than 5.5% residue at 600° C., for example, less than 5% residue,less that 4% residue, less than 3% residue, less than 2% residue, orless than 1% residue or lower.

Second Precursors

It will be understood by one skilled in the art that any number ofsecond precursors may be used in the vapor deposition processesdisclosed herein, depending on the desired W containing film to bedeposited. In some embodiments a second precursor may be an oxygenprecursor, or oxygen containing reactant. In some embodiments a secondprecursor may be a nitrogen precursor, or nitrogen containing reactant.In some embodiments a second precursor may be a chalcogen precursor, orchalcogen containing reactant. In some embodiments the second precursormay not significantly contribute material to the final formed film.

In some embodiments an oxygen precursor may comprise, for example, O₂,H₂O, O₃, and/or other oxygen-containing compounds. In some embodimentsan oxygen precursor may comprise oxygen plasma, oxygen radicals, oroxygen atoms. In some embodiments a nitrogen precursor may comprise, forexample, N₂, NO₂, NH₃, and/or other nitrogen containing compounds. Insome embodiments the nitrogen precursor may comprise nitrogen plasma,nitrogen radicals, or nitrogen atoms.

It will be understood by one skilled in the art that any number ofchalcogen precursors may be used in the vapor deposition processesdisclosed herein. In some embodiments, a chalcogen precursor is selectedfrom the following list: H₂S, H₂Se, H₂Te, (CH₃)₂S, (NH₄)2s,dimethylsulfoxide ((CH₃)₂SO), (CH₃)₂Se, (CH₃)₂Te, elemental or atomic S,Se, Te, other precursors containing chalcogen-hydrogen bonds, such asH₂S₂, H₂—Se₂, H₂Te₂, or chalcogenols with the formula R-E-H, wherein Rcan be a substituted or unsubstituted hydrocarbon, for example a C₁-C₈alkyl or substituted alkyl, such as an alkylsilyl group, or a linear orbranched C₁-C₅ alkyl group, and E can be S, Se, or Te. In someembodiments a chalcogen precursor is a thiol with the formula R—S—H,wherein R can be a substituted or unsubstituted hydrocarbon, such as aC₁-C₈ alkyl group, or a linear or branched C₁-C₅ alkyl group. In someembodiments a chalcogen precursor has the formula (R₃Si)₂E, wherein R₃Siis an alkylsilyl group and E can be S, Se, or Te. In some embodiments, achalcogen precursor comprises S or Se. In some embodiments, a chalcogenprecursor comprises S. In some embodiments the chalcogen precursor maycomprise an elemental chalcogen, such as elemental sulfur. In someembodiments, a chalcogen precursor does not comprise Te. In someembodiments, a chalcogen precursor does comprise Se. In someembodiments, a chalcogen precursor is selected from precursorscomprising S, Se or Te. In some embodiments, a chalcogen precursorcomprises H₂S_(n), wherein n is from 4 to 10.

Suitable chalcogen precursors may include any number ofchalcogen-containing compounds so long as they include at least onechalcogen-hydrogen bond. In some embodiments the chalcogen precursor maycomprise a chalcogen plasma, chalcogen atoms or chalcogen radicals. Insome embodiments where an energized chalcogen precursor is desired, aplasma may be generated in the reaction chamber or upstream of thereaction chamber. In some embodiments the chalcogen precursor does notcomprise an energized chalcogen precursor, such as plasma, atoms orradicals. In some embodiments the chalcogen precursor may comprise achalcogen plasma, chalcogen atoms or chalcogen radicals formed from achalcogen precursor comprising a chalcogen-hydrogen bond, such as H₂S.In some embodiments a chalcogen precursor may comprise a chalcogenplasma, chalcogen atoms or chalcogen radicals such as a plasmacomprising sulfur, selenium or tellurium. In some embodiments theplasma, atoms or radicals comprise tellurium. In some embodiments theplasma, atoms or radicals comprise selenium.

Example 2

WS₂ thin films were deposited according to ALD processes describedherein at 300° C., 350° C., and 500° C. A F120 ALD reactor (ASMMicrochemistry) was used to deposit the WS₂ films. W(thd)₄ was used asthe W precursor and H₂S was used a second precursor. Sample WS₂ filmswere deposited on silicon, Al₂O₃, and ZnS substrates. The WS₂ samplefilms were deposited using an ALD process including 2000 depositioncycles, with each cycle having a W precursor pulse time of 1 second anda second precursor pulse time of 2 seconds, separated by 1 secondnitrogen purges. The W(thd)₄ was evaporated from an open glass boat thatwas heated to between 160° C. and 165° C. inside the reactor.

Energy dispersive X-ray spectrometry (EDX) was used to analyze the filmsand it was found that the films contained W and S. No indications of thepresence of crystalline material were found when the films were analyzedusing X-ray diffraction (XRD).

The sample films deposited at 350° C. were also analyzed using XRD. Asshown in FIG. 5A, these sample films showed a broad peak centered near13° (20) that was identified as WS₂. The crystallinity of these sampleWS₂ films was confirmed via scanning electron microscopy. As shown inFIG. 5B, flakes of crystalline WS₂ were observed on the substrate. Someslight decomposition of W(thd)₄ was observed inside the reactorsubsequent to film deposition. Film samples deposited at between 300° C.and 350° C. had an estimated thickness of about 2 nm, as calculated fromEDX data.

A WS₂ film sample deposited at 500° C. and according to the parametersdescribed above, but including a 0.2 second W precursor pulse time werecrystalline, although decomposition of W(thd)₄ did occur. As illustratedin FIG. 6A, XRD analysis showed a high intensity peak identified ascrystalline WS₂. The sample film was found to be about 10 nm thick. Ashown in FIG. 6B, SEM analysis revealed large thin crystalline flake.Some of the flakes were observed to be perpendicular to the substratewith lateral dimensions on the order of 200 nm. The sample filmcomposition was determined via EDX and was found to be 32 at % W, and 68at % S, which was within the experimental error for the theoreticalvalues for WS₂ (33.3 at % W, 66.6 at % S).

2D Materials

The vapor deposition processes described herein may be used to deposit2D materials comprising W, for example W dichalcogenides such as WS₂ orWSe₂ 2D materials. 2D materials, also referred to as single layermaterials, are materials that consist of a single connected molecularmonolayer. While 2D materials form a single connected molecularmonolayer, multiple monolayers may be deposited by the depositionprocesses disclosed herein. For example, in the case of 2D WS₂, the 2Dmaterial comprises a single layer of covalently bonded WS₂ molecules,arranged so that one layer of W atoms is sandwiched between two layersof S atoms. The basic atomic structure of a WS₂ will be familiar to theskilled artisan.

Due to their unusual characteristics, 2D materials are useful in a widevariety of potential applications, for example as lubrication, inoptoelectronics, spintronics and valleytronics, in THz generation anddetection, for use as catalysts, chemical and biological sensors,supercapacitors, LEDs, solar cells, Li-ion batteries, and as MOSFETchannel materials.

Unlike other 2D materials such as graphene, 2D W dichalcogenides possessunique electronic properties that make them useful for semiconductordevice miniaturization. For example, unlike graphene, 2D Wdichalcogenides have a direct band gap and are semiconducting.Therefore, W dichalcogenides are useful in electronic devices, forexample W dichalcogenides can be used as a channel material in a gatestack or transistors.

According to some embodiments a 2D material comprising W can bedeposited by vapor deposition according to the methods disclosed herein.In some embodiments a 2D material comprising W may comprise less than orequal to ten molecular monolayers of a compound comprising W, less than5 molecular monolayers, or less than or equal to 3 molecular monolayers.

In some embodiments the 2D material comprising W may comprise less thanor equal to ten molecular monolayers of a W dichalcogenide, less than 5molecular monolayers, or less than or equal to 3 molecular monolayers.In some embodiments the 2D material comprising W may comprise less thanor equal to ten molecular monolayer of WS₂, WSe₂, or WTe₂, less than 5molecular monolayers, or less than or equal to 3 molecular monolayers.

In some embodiments a method for depositing a 2D material comprising Won a substrate may comprise a deposition process as disclosed hereincomprising multiple cycles. In some embodiments a method for depositinga 2D material comprising W may comprise at least one deposition cycle,up to about 500 deposition cycles, up to about 200 deposition cycles, orup to about 100 deposition cycles. As can be selected by the skilledartisan depending on the particular precursors, substrate and processconditions, a method for depositing a 2D material comprising W on asubstrate may comprise an ALD process as disclosed herein comprisingless than or equal to 50 cycles, less than or equal to 25 cycles, lessthan or equal to 15 cycles, or less than or equal to 10 cycles.

In some embodiments the deposited 2D material comprising W may be lessthan 10 nm, less than 5 nm, less than 3 nm, less than 2 nm, less than1.5 nm, or less than 1.0 nm.

In some embodiments material comprising W, such as a 2D material, isable to be used in an electronic device, for example as the channelmaterial in a gate stack. In some embodiments a material comprising W,such as a 2D material, may be deposited after the gate dielectric, thatis, channel-last. In some embodiments a material comprising W, such as a2D material, may be deposited prior to the gate dielectric, that is,channel-first. In some embodiments the gate stack may be manufacturedupside down, such that the channel is above the gate in the gate stack.

As used herein, the term “about” may refer to a value that is within15%, within 10%, within 5%, or within 1% of a given value.

The terms “film” and “thin film” are used herein for simplicity. “Film”and “thin film” are meant to mean any continuous or non-continuousstructures and material deposited by the methods disclosed herein. Forexample, “film” and “thin film” could include 2D materials, nanorods,nanotubes or nanoparticles or even single partial or full molecularlayers or partial or full atomic layers or clusters of atoms and/ormolecules. “Film” and “thin film” may comprise material or layer withpinholes, but still be at least partially continuous.

The term chalcogen as used herein is meant to refer primarily to thechemical elements sulfur, selenium, and tellurium, although in somecases, as will be clear to those of ordinary skill in the art the termmay also refer to oxygen. Similarly, the terms chalcogenide anddichalcogenide are mean to refer primarily to sulfides, selenides, andtellurides, although in some cases, as will be clear to those ofordinary skill in the art such terms may also refer to oxides.

It will be understood by those of skill in the art that numerous andvarious modifications can be made without departing from the spirit ofthe present invention. The described features, structures,characteristics and precursors can be combined in any suitable manner.Therefore, it should be clearly understood that the forms of the presentinvention are illustrative only and are not intended to limit the scopeof the present invention. All modifications and changes are intended tofall within the scope of the invention, as defined by the appendedclaims.

What is claimed is:
 1. A compound having the formula WL₄, wherein W hasan oxidation state of +IV, and L is a beta-diketonato ligand.
 2. Thecompound of claim 1, wherein L comprises2,2,6,6-tetramethyl-3,5-heptanedionato (thd).
 3. The compound of claim1, wherein L comprises trifluoroacetylacetonato (tfac).
 4. The compoundof claim 1, wherein L comprises hexafluoroacetylacetonato (hfac).
 5. Thecompound of claim 1, wherein L comprises2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedionato (fod).
 6. Thecompound of claim 1, wherein L comprises acetylacetonato (acac).
 7. Avapor deposition reactant comprising a tungsten compound having theformula WL₄, wherein W has an oxidation state of +IV and L is abeta-diketonato ligand.
 8. The vapor deposition reactant of claim 7,wherein the reactant is in the vapor phase.
 9. The vapor depositionreactant of claim 7, wherein the reactant does not comprise a solvent.10. The vapor deposition reactant of claim 7, wherein the tungstencompound is W(acac)₄ where acac is an acetylacetone ligand, W(hfac)₄where hfac is a hexafluoroacetylacetone ligand, or W(thd)₄ where thd isa 2,2,6,6-tetramethyl-3,5-heptanedionato ligand.
 11. The vapordeposition reactant of claim 7, wherein the tungsten compound isW(thd)₄, where thd is a 2,2,6,6-tetramethyl-3,5-heptanedionato ligand.